Railway signaling system



Oct. 19, 1943. THOMPSON 2,332,279

' RAILWAY SIGNALING SYSTEM Filed Jan. 8, 1943 5672! v 61574:: L1 507 1 i 3 I BX INVENTOR 631. Muzz- HIS ATTOI-IQNEY Patented Oct. 19, 1943 I UNITED STATES PATENT OFFICE r 2,332,275 7 I Y it RAILWAY SIGNALING SYSTEM:

Howard A. Thompson, Edgewood, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application January 8, 1943 Serial'No. 471,681

' ite ('01; 24 -63) My invention relates to a railway signaling system of the type inwhich coded alternating current energy is supplied tothe rails of a track section to control cab signal apparatus on a lo comotive-in the track section.

In systems of this type coded energy of a distinctive code frequency, as for example, energy of 75 code frequency, is supplied to the rails of the track section in the rear of an occupied section to cause the cab signal apparatus .on a loco motive in that section to display a restrictive proceed indication, as for example anapproach indication. -I-lowever, with previoussystems of this type the engineer has no means of knowing when he is approaching the end of the section in the rear of an occupied section unlesswayside signals or markers are provided to'marl; the limits of the track sections, since the locomotive cab signal apparatus will provide the"approach indication until the locomotive enters the occupied'section.

, .An object of this invention is to provide asys-j tern of the type described which is arranged so that the cab signal apparatuson a loco-motive in the adjacent section in the rear of an occupied section will display its approachindication until the locomotive advances to within a predeter mined distance of the exit end of the's ection','and

so that the locomotive cab signal apparatus will" thereafter displayits; most restrictive indication. 0 Another object of the inventionistoprovidea? system of the type described. and incorporating means to supplyto thejs'ection rails duringcthel off periods in the code, alternatingcurrent eiifergy of substantially lower voltage than that'sup plied to the section rails during the on periods in the code to thereby prevent operation of code responsive apparatus on a locomotive in the secthen point out the novel features thereof in claims. V -In the drawing, i Fig. l is a diagram of a section of railway track equipped with apparatus embodying my in-' vention, and; -.Fig. 2 is a diagram of a modification which I may'employ. r 'Similarreference characters refer to similar partsinboth views. I i. v

In practicing my invention I- provide aprin cipal track transformer from which there is supplied to the rails of a track section during the picked-up periods of the contacts of a coding de-; vice energy oia voltage effective to operatethe cab signal apparatus one, locomotive at any point in the track section. In addition, I provide an auxiliary track transformerfrom which there is supplied to the rails of a section during the re-' leased periods of the coding device contacts, when the adjacent section in advance is occupied; energy of a, lower voltage which is effective to operate the cab signal apparatus on a locomotive.

only 'after the locomotive has advanced to within a predetermined distance of-theexit end of thesection, while'l provide a relay governed by tion only after the locomotive hasadvanced a.

substantial part of the distance towardsthe exit end of the track section. P

A further object oftheinvention is to provi e a system of the type described and incorporating means to check the supply of energy to the section rails during the oii periods in the code and to preventthe supply of energyto the section rails during the on periods in the-code unless energy is also supplied to the section rails during the oil periods in the code.

'Other'objectsof' the invention and features of novelty will be apparent from the'following' description taken in connection with theaccoinpanying drawing. V

I shall describetwo forms of railway signaling apparatus embodying my invention, and shall supply oi, energy from the auxiliary track transformer to the section ralis and controllingflthe supply ofen'ergy to the principal track transformer.

Referring to Fig. 1 of the drawing, there is shown therein a stretch of railway trackhaving track rails I and.2 over which traffic normally. moves in the direction indicated by the arrow, th'atis, from leftto right. The rails of the track stretch are divided. by insulated joints 3 into track sectionsfor signalingpurposes. Onesuch sectiom'whioh is designated ST, and portions of the adjoiningsections 4T and GT, are shown in,

the drawing.

Asshown, the track stretch is without wayside signals and movement of trains through" the track stretch is governed by cab signal appar a ed primarily for use in track stretches having cab signals only, it is not limited to use insuch situations, and is equally applicable to track stretches equipped with Wayside as Well as cab signals.

of this; invention and any appropriate form of apparatus maybe employed forthis purpose.

" One form of cabfsignal apparatus which may be employed is shown in Letters Patent of the United States No. 1,986,679, granted January 1, 1935, to Lloyd V. Lewis. The apparatus shown in that patent includes receiver coils mounted on the locomotive over the track rails in advance of the leading wheels of the locomotive. Alternating energy supplied to the track rails at the exit end of the section flows between the tracl; rails through the"'whellsland axles 'of the locomotive, while this energy flowing in the portions of the track rails beneath the receiver coils causes en; ergy to be induced in the receiver coils. The en'- ergy induced in the receiver coils is amplified and. is employed to operate signal apparatus on the locomotive. The locomotive equipment is arranged so that it will operate to provide 'aprocd signal indication only when coded or periodically CT which have contacts which are actuated between their picked-up and released positions at rates such as to provide coded energy consisting of 180 or 75 energy impulses which are separated by periods of substantially equal duration in which no energy is supplied.

The alternating current supplied to the track tr estermera be u p ied 3 m, .any me source, not shown, the terminals of which are designated BX and CX in the drawing.

The equipment at each end of the track section includes a source of direct current, not shown, the terminals of which are designated B and C.

The e'quip ment is shown in the condition which it assumes when the track stretch is vacant. At this time t elrel ay GE is picked up and its contact l fi es tab lishs'the circuit controlled by code interrupted energy is supplied thereto, and so that it will provide its most restrictive indication when no energy or steady energy is supplied thereto.

In addition, in order to prevent response of'the, locomotive cab signal apparatus to foreign current, the equipment. on the locomotives is:arranged so that it will respond to energy in the track rails only when the energy inthe portion of the track rails beneath the receiver coils exceeds a predetermined'minimum. This'val'ueis determined by the amount of current flowing between the track rails through the wheels and axles of the locomotive, and is termed the-axle current.

The track section 5T is provided with a". track circuit comprising a code following traclr relay 5TB to which is supplied coded circuit current from atrack battery 5TB. Means isprovided for supplying coded energy to the section rails from 'a principal track transformer 5TB, and to. also supply energy to the section rails from the auxiliary"tra'ck transformer ETTA over a ci-rcuit which includes an auxiliary relay, 55R in series therewith.

The principal track transformer STI were; portioned so that the voltage of the energy sup plied from the secondary vwinding thereofto the section rails is such as to cause the axle current at the entrance end of the section to be high.

enough to insure operation of the cab signalapf paratus on'a locomotive at the entrance end of the section under the most adverse ballast "conditions.

The auxiliarytrack transformer ETTA is. pro;

portionedso that the voltage of the energy sup plied from'the secondary winding thereof tovthe trackrails is such as to'cause too little axle cur rent to flow in the'portion of the section. adjacent the entrance end of the sectionfto ar feet the cab signal apparatus on a locomotive, As

a locomotive advances in the track. section'the value of the axle current produced by energysuplplied from both transformers increases, arm w n the locomotive reaches, a point some distance such as 2500 feet, from the exit end o f lthe s x tion, the axle current resulting from energy sup plied from transformer 5TTA 'will increase to Lia value efiective to operate the locomotive cahfsig;

nal apparatus.

Thesupply of energy to the track section is governed by a coding relay ECTM, while the js ply of energy to relay SCTM is governed by a e,-- lay 6H which is governed by trailic conditionsiin section 6T so as to be picked up or. released'a'ce cording as section GT is vacant or is occupied The relay 6H has associated therewith' con;

h ail i arm-am B n r m e Pr n a i e ka i fifiimmfi 5T1.- During .the releasedperiods Iof: contact; 12

r ay c'lM- iie u he eecn e-mw nd:

iu ia e -k tran former; 52 s: tablished, but ias-the circuit of the prirnarywinding of, transforif n er dTTA' is interruptedbyrontact ll of relay BHenerg -visnot ipplied from e ier r. T AtQ-F LC-SQGF QFl a.

The efirgr u pl ed rem a.-. t ery are 0. h ee mils eed p.to ra k; ay 5TB and operates it I so that: energy. is supplied; through the l i s eshin -(5D? m elay. in. in the manner explained in Letters Patent supply of energy 'to'the rails of section: 41 in the same manner. that relay,6H con-t'rols the supply of energy to. sectionj'l.

W eaa train mo i gn e crmel; ir e i m ofgtrafiic enters section- 5T, the track .relay 5TB. ses, t llow ode. nd re a e es a- In. addition. when the .train enters section 5T1 the coded alternating ,currenthi 180 code frequency supplied fro'm the, principal track. transformer STT toith'e rails ofjs'ectioh, 5T,0pe 2ates the eal signal. apparatu on. the locomotive l of, the t fi in so that a clear s nalis displayedin the locomotive cab. I

s po ntedput; above. e e gy is, ,no u pl ed. r m'f he. l l l w rack. f rm r T-TA the section rails; a: this; time. I Accordingly. th

Icab'signal' apparatus on the. locomotiv of th t a n in section, 5T will operate in the custo'mary mQiUD-GftO provide theclear signal indicationvas; the locomotive ,proceedjs through the,.-track. .sec;- i v V H ea e e it wntact rans e st nt el: of coding. relay so'r vr from tnelco ta t or. code... transmitter ISOCT to the contact of .codeftranlsg, .mitter Tv In addition, contact l-.I of relayfifl interrupts the, circuitestablished by, its front son tact for, supply-ins ner Q-ihe. c pa ,t k. transformer 5TT and establishes.. a..,circuit for...

supplying energy to the auxiliary tra ktran 'When' the train. enters section ,GIIY, the relay;

Theiocomotive cab signal'equipmentcmustzbe former providedzthe contact of relay EAR is supplied with coded energy inorder to provide vpickedeup. J

As energy is 'suppliedto theprimar y windingof the auxiliary track-transformer .BTTA, energy is supplied to. the, section rails from the secondary winding of thistransformer over the circuitwhich is traced from one terminal of the transformer secondary, winding to rail I, and from the other terminal of the transformer secondary Windin through ,one leg of the rectifier R, winding of auxiliary relay, SAR, another. leg of the rectifier 5R, andbackcontact 112 of relay 5CTM torail 2. As a resultof the supply ofenergyfromtransformer STTA to the section railsv over the circuit which includes thewinding of relay BAR in. series therewith, contact [4 of relay EAR is picked up and-establishes a circuit to supply energy tothe Accordingly, when section-:61 'isroccupiedfand.

relay 6H is, released, coding relay 'SCTM is operated at the '75 code speed, while energy is supplied from transformer ETTA to, the section rails during the released periods of contact I2 of relay SCTM, and energy is supplied tothesection rails from track battery 5TB and the transform'erETT during the pickedeup periods of contact l2.

When the train under consideration vacates section 5T, the energy supplied from track battery 5TB to the section rails, feeds to track relay 5TB. and operates it so thatenergy is supplied throughthe decoding transformer 5DT to relay 5H. When thetrain advances far enough to vacate sectionfiT, relay, 61-1 is picked up'andtransfers control of relay SCTM from code transmitter TSCT to code transmitter JBDCT, while contact ll of relay; 6H;interrupts the circuits forsupplying energy to transformers, 5TTA and I ETT andestablishes the circuit for supplying energy to the transformer 5TT. v e v If while a train is in section 6T a second train ter i e nfi'l' he ca si equipment e1 the locomotiveof the second train will respond to the energy of75 code frequency supplied from the principal track transformer 5TT to the section rails and will provide theapproach indica tion aslong as thetrain isinthe portion Of'SGC tion 5T adjacent the entrance end of the section.

At this time energy is also suppliedfto the sec tionlrails from theauxiliary tracktransformer BTTAQbutas explained above, the voltage of the;

energy supplied from the auxiliary track transformer is so low that energy supplied from this transformer has no effecton the cab signal equip ment on a locomotive in the portion of section adjacent the entrance end-of the section.

' Whenthe train advances to within a predetermined distance of theexit end ofsection,5T,

cation.

a proceed indication, and when steady energy. is supplied thereto the locomotiveequipment operates to provide its stop Accordingly, when a train enters the section .in the, rear offlan occupied section, the cab signal equipment on; the locomotive, of the train or mostv restrictive indication. This will inform the engineer on the locomotive of the factthat he is approaching the end of the track'section and is about to enter an occupied section. .The'oper- .ation of the system, therefore, is such that the occupied section.

cab signal apparatus on a locomotive operatestoiprovide the most, restrictive indication while The pointto which a train must advance'in the section before the current supplied from transformer ETTA increases to a value eiTe'ct-ive .to operate the locomotive cab signal apparatus will. vary with changing ballast conditions, The various parts of the apparatus may be selected and adjusted so that under the most adverse ballast conditions the energy supplied from transformer ETTA will operate the cab signal apparatus on a locomotive for at least the selecteddistance, such as 2500 feet from the exit end of the section, so that a train will always have at least this much Warning that it is approaching the end of the section. 7

Under favorable ballast conditionsthe energy supplied from the auxiliary track transformer ETTA will be effective to operate the cab signal apparatus on a locomotive somewhat farther than the minimum distance of 2500 feet from the en.-

tranceend of the track section. Accordingly, under favorable ballast conditions a train will receive the restrictiveindication somewhat soon.- er than it is received under adverse ballast conditions, but as. a train will always receiv the minimum warning thatit is approaching an occupiedsection; the system is entirely safeand variations in the point at Which the restrictive I indication is given are not objectionable:

If'there should be a failure in the supply of energy from the auxiliary track transformer continue to provide the approach indication throughout the entire length of section ST, and the equipment would fail to operate in the nor- ,malrnanner to warn the engineer when his train approaches an occupied section; This system includes means to prevent such a failure.

In the system shown in Fig. 1, energy is sup;-

plied fromth auxiliary track transformer ETTA to the, section rails over a circuit Which includes the winding of relay EAR. in series therewith, so that contact [4 of relay SAR is picked up when and only when energy is supplied from trans; former 5TTA to the section rails. Contact M of relay 5AR controls the supply of energy to transformer 5TT,so thatwhen relay 6H isreor most restrictive indileased, energy will not he supplied to transformer .-5'I'I', and, therefore, will not be supplied from transformer 5TT to the section rails, unless energy is being supplied from transformer 'S'ITA to thesection rails. This insuresthat when .a train enters section 5T at a time when section GT is occupied, energy will not be supplied from :transformer 5T1 to the section rails to cause the displayof the approach indication by. the locomotive cab signal equipment when'the train is in the portionof the track sectionadjacent .the entrance end of the section unless energy also supplied to the section rails from transformer 5'ITA to cause the locomotiv cab signal equip- .ment to provide its most restrictive indication i when the train advances into the portion of the track section adjacent the xit end of the section.

Accordingly, if for any reason energy is not supplied from transformer 5TTA to thesection rails when section GT is occupied, the cab signal apparatus on a locomotive will display its most restrictive indication as soon as 'thelocornotive enters section 5T and the engineer have ample warning that he is approaching an occupied section.

The system provided by this invention is also adapted for use in track stretches in which coded alternating current energy is employed in the track circuits to operate the track relays as well as for the control of cab signals, and 21s a diagram illustrating such a modification.

The system shown in Fig. 2 is similar to that shown in Fig. 1 but differs there-from in that the track relay 5TB, is connected to the track rails through .a transformer and a rectifier, While the transformers B'IT and ETTA are connected-to the track rails through :a transformer 5ST. stead of being directly connected to the section rails.

The equipment is shown in the condition which it assumes when the track stretch is vacant. At this time relay 6H is picked :up and its contact 'Hl establishes the circuit cont-rolled by a contact of code transmitter HJBCT for supplying energy from the principal transformer 5TT .to traznsformer EST and thus to the section rails. The energy sup-plied from transformer to the section rails feed to the track relay TH .and operates itso that energy is supplied through the decoding transformer :5'DT .to relay :SH-to keepithe contacts of relay 5H picked up,

When a train moving in the normal direction of traffic enters section ET, the track relay is shunted and relay Eli-releases, while ;the',cab signal apparatus 'on the locomotive of the brain responds :to the coded alternating current energy supplied to the sectionrails and provides theolear indication. H U 5 When the train advances into sect/lentil; relay ,SHr eleases and contact I 0 interrupts-the ci-rcuit controlled by .thcflcontact of code transmitter IBEZC'I for supplying energy to. the rails .of sec .tion 5T, and establishes the circuit .controlle dby .a contact of code transmitter LECT. the" released periods of the contact of coder .T.5 C.'I energy is sup-plied from transformer B'I'TAflto transformer EST-over .the circuit including the retitlfier SR and the winding of relay in series therewith. Accordingly, contact I14 of, relay EAR is picked up so that during the picked up periods 'of the contact of code transmitter 'E'SCT energy is supplied "from transformer "EI-T to transformer 5ST over the circuit which includes front contact Hi-of relay EAR. The nergy supplied from transformer SEPTA to the section rails is of substantially lower volt.-

age than that supplied from transformer STT, and .is or such value that too little energy is supplied therefrom to the track relay 5TB to maintain the contacts of the track relay picked up. Accordingly, whensection 5'1 is' vacated, the. ,contactsof relay 5TB. pickup during the picked.-

up periods of code transmitter 1.501, at which time energy issupplied from transformer"5TT, whlle'the contactsoi relay 5TB release during the released periods of coder "CT, at which time energy is supplied from transformer ETTA. As -a result of code iollowing operation-of relay 'STR energy :is supplied through :the decoding transformer EDT and they contacts of ma 5'H'are picked up.

.When the train waca-tes section 5T, relayBH picks "up and its contact 10 transfers control of the supply or energy to section H from coder 156T tocoder lMCTand energy of I code frequency is supplied from tranStortner'i'IT to the section rails, while the supply or energy from transformer 5TTA to the section railsiis' cut 01f and. relay BAR releases. 1

If while sections; is occupied a second train enters section 5T, the cab signal equipment on the locomotive of second train -will respond to the energy of 15 code frequency supplied transformer EB'IT to the section rails and will pro- }Vide the approach indication as long as the train is in the-portion of section 5T adio-cent the entance inthe track section, the energy from transformer ETTA-flowing in the track rails beneath the receivers on the locomoti-ve will increase to a value high enough to operate the cab signal apparatus and the indication provided -'-by the cab signal equipment will be changed from the approach to'the stop or most ES ZrictiV-e indication. If, for any reason, energy-is not supplied from transformer fiT'TA tothe section rails when section 8T is occupied, relay will *be released and will prevent the su-pply of energy from transformer to the section raiils. prevents the display of the approach indication by the cab signal apparatus on a-locomotive in-the por t-ion of section ET adjacent the entrance end of the section unless the waysideegnipment-is 'f-unctioni-ng' -i n'-th'e' proper manner to cause the locomotive cab signal apparatus to display its most restrictive indication when the lecomotive advances into the port-ion of the track section adjacent the exit end of the section. i r

Although-I have herein shown and described only two forms of railway signaling apparatus embodying my invention, it i unders'tood that various changes and modifications may be made therein within-the-scepe of the appended claims without departing from the spirit and scope of my invention. w a

Having thus described my invention, what I claimis: p

fl. In combination, a section of railway track throughwhich are operated-locomotives equipped with cab signal apparatus "responsive to flow'of alternating current in excess pf :a predetermined value in the track rails'in advance of {the jloco-i motive and effective to provide a proceed -i-ndi'- cation only when said alternating, currentfis 'coded, and means for alternately supplying to the section rails at the exit end of the section impulsesof alternating current energy ofav oltage high enough to cause energy in' excess of. said predetermined value tobe present. in the.

alternating current in excess of a predetermined. value in the track rails in advance of the locomo tive and effective to provide a proceed indication only when said alternating current is coded, a first source of alternating current of a voltage high enough to cause energy in excess of said predetermined value to be present in the section rails throughout the section, asecond source of alternating current of a voltage effective to cause energy in excess of said predetermined value-to be presentv only in the portion of the section rails within a predetermined distancefrom the exit end of'lthe section, and means for alternately supplying to the track rails at the exit end of the section'impulses of energy from said first and said 'seconds'ources. a

73. In" combination, *a-s'ection of railway track throughwhich are operated locomotivesequipped with cab signal .apparatusrespo-nsive to flow of alternating current in excess ofa predetermined; value'in the track rails in advance of the locomotive and effective to provide a proceedindication only when said alternating current" is coded, a first source of alternating current of a voltage high enough to cause energy in, excess of said predetermined value 'to'be present in the section rails throughout'thesection a second source of I alternating current of a voltage eifectivetocause I energy in excess of'said predetermined value to be present only in the portion of the section rails withinja predetermined distance from the exit end of the section, means forsupplying from said first'sourceto the section rails at the exit end of the section impulses of energy which areseparated by'foif periods during which the supply section during the ofi periods in the supply of energy from said-first source. I

4. In combination, a section of railway track through which are operated locomotives equipped with cab signal apparatus responsive to flow of alternating current in excess of a predetermined value in the track rails in advance of the locomotive and efiective to provide a proceed indication only when said alternating current is coded, a

first source of alternating current of a. voltage high enough to cause energy in excess of said predetermined value to be present in the section rails throughout the section, a second source of alternating current of a voltage effective to cause energy in excess of said predetermined value to be present only in the portion of the section rails within a predetermined distance from the exit end of the section, means for supplying from said second source to the section rails at the exit end of the section impulses of energy which are separated by 0 periods during which the supply of energy from said source is interrupted,

,50, of energy from' saidfirst source is interrupted, and means for supplying energy from said second source to the section rails-at the. exit end of the and means responsive :tothe supply of' energy from said second source of energy to'the section rails for supplying energy from said first source to'thesectionrailsfat the'exitend of the section" during the o periods inf the supply of energy from said second source to the section rails.

5. Incom bination, a section of railway track through which are operated locomotives equipped with cab signal apparatus responsive to flow of alternating current in excess of a predetermined value in the track rail'sj in advance of the loco motive and effective to provide a proceed indication only when said alternating current is coded, a first sourceof alternatin'g currentof a, voltage highfe'nou'ghto cause energy in' excess of said predetermined value to be present in the j section rails throughout the section, a second source of alternating'current of a voltage effect-' tivev to cause energy in excess of said predeltergi mined ,value to present only in the portioni 'of the section rails wit in-a predetermined distance from the'exit end of the section andfacoding,-

device having a'contact continuously movedbe-' tween a f rst and a'seco'nd position, a contactioi" said coding -device being effective when' in its first position to establish a circuit for supplying energy from; said first source tothe sectionf rails at'the exitend ofthe section; a Contact of said:

coding device being effective when in its second position top establish a circuit for supplying energ'y'from saidseco'nd source tothe sectionflrailsfl at thefexit endof thesection.

' 6. In 'combination a section ofjrailway track through which are 'operated'locomotivesequipped with cab signal apparatus-responsive to 'flow" of alternatingcurrent' in excess ofa predetermined value in 'the track-rails in advance jqf fithe' locomotive nd 'efi'ective vto provide a proceed 'indi cation only when said alternating; current is" coded; a first sourceof alternating c1 1' rrent of a voltage high enough to cause energy inexcessjcf 'f I said predetermined value tobe presentin the section rails throughout the 's'ec ti'cn, a" fsecond sourceer alternatingmurrent of a voltage eif e tive tocause energy in excess of said predete'ra mined valuetobe present only in the portion of the section rails within a predetermined'distance fromthe exit endor thesectiong'ja'codingdevice 'havinga c'ontact continuously moved between a v position, a contactof said'cod ing device bein'giefiotive when in its/first posi J tion' to'e'stablish a circuit for supplyingf-energyif from-said first sour'ce' tothe'section ra'il'sat the exit'end of the' section, a contact of'said'co'ding device'beii-igefiectiv when in-its second pos itiori' to establish a circuit for supplying energy fro m said second sourceto the section rails at the exit end of the section, and means responsive to the supply of energy from said second source to the section rails and controlling the supply of energy from said first source to the section rails.

7. In combination, a section of railway track I through which are operated locomotives equipped with cab signal apparatus responsive to flow of alternating current in excess of a predetermined,

end of the section, and a coding device having contacts continuously moved between a first and a second position, a contact of said coding device being effective when in its second position to establish a circuit for supplying energy from said second source to the section rails at the exit end of the section in series'with the winding of an auxiliary relayfa contact ofsaid.coding device being. effective when in itsufir'st position to establish a circuit including a front contact of said auxiliary relay for supplying energy from said first source to the section .rail's at. the exit end of the section.

8. In combination,.a stretch of railway track through which are operated locomotives equipped,

with cab signal. apparatus responsivev to flow of alternating current in excess of a. predetermined value in the track rails iniadvance of the locomotive and effective to provide aproceed indication.only when said alternating current is coded,

the rails of said track stretch being divided by insulatedjoints into a plurality of track sections including a forward and -a rearward section, afirst source of alternating current of avoltage high enough tocause energy in excess of said predetermined value to bepresent throughout the rails of a track section, a. secondisource of the rails of said rearwardsection at the exit end of said section energy from said first source coded at a first rate, and means effective when said forward section is occupied to supply to the rails of said rearward section at the-exit end of said section energy from said first source coded at a second rate and to also supply tothe section rails energy from said second source in the periods between the impulses of coded energy supplied from said first source. 3 V

' 9. In combination, a stretch of railway track through which are operated locomotives equipped with cabv signal apparatus responsive to flow of alternating current in excess of a predetermined value in the track rails in advance of the locomotive and effective to provide a proceed indi-- cation only when said alternating current is coded, therails of said track stretch being divided;

by insulatedjoints into a plurality of trackseetions includinga forward and a rearwardsection, a first source of alternating current of a voltage high enough to cause energy inexcess" of said.

predetermined value to bepresent throughout the rails of a track sectionla second sourceof alternating current of avvoltage effective to cause energy in excess of said predetermined value to be present only in the portion of the rails of a 5 section within a predetermined distance from the exit end of the section, means effective when of an auxiliary relay energy from said first source,

coded at a second rate and to'also supply to the rails of said rearward section over a circuit including the winding of said auxiliary relay in series therewith energy from said second source in the periods between the impulses of coded energy supplied from said first source.

10. In combination, a stretch of railway track through which are operated locomotives equipped with cab signal apparatus responsive to flow of alternating current in excess of a predetermined value in the track rails in advance of the locomotive and effective to provide a proceed indication only when said alternating current is coded, the rails or said' track stretch being divided by insulatedjoints into a plurality of track sections including a forward and a rearward section, a

first source of alternating current of a voltage high enough to cause energyin excess of said predetermined value to be present'throughout the rails of a track section, a second source of 5 alternating current of a voltage effective to cause energy in excess of said predetermined value to be present. only in the portion or the rails of a section within a predetermined distance from the exit end of the section, means efiective when said 40 forward section isoccupied to supply to the rails,

of said rearward section at the exit end of the, section over a circuit including the front'contact,

of an auxiliary relay energy from said firstisource coded at a second rateand to also supplyto the rails of said rearward'sectionover a .circuitin- I cluding the winding of said auxiliaryrelay in series therewith energy from said second source in the, eriods between the impulses of coded energy supplied from said first source, and means effective when said forward section is vacant to supply'to the railsof said rearward sectionjat. the'exit end of the section over a circuit inde,

pendent of said auxiliary relay energy from said first source coded at a first rate.

HOWARD A. THOMPSON. 

